Before being filled with a liquid food or other products, bottles or similar containers are usually subjected to several preliminary treatment steps, particularly to a thorough cleaning and optionally sterilization. To improve the microbiological quality of filled liquid foods, it is known to sterilize the bottles with heat, prior to the filling operation, to kill any germs that may be present and that are dangerous to the food in question. This occurs, in general, by the introduction of steam, hot water or superheated water into the bottle to be sterilized by means of a sterilization installation with spray nozzles, which installation is generally connected as a separate machine before a filling machine, or, in individual cases, it is integrated into the filling machine. However, an incorrect course of the process cannot be completely ruled out. Thus, as a result of a failure of control valves, or insufficient pressure, the killing of the germs in the bottle to be sterilized can be insufficient, or completely absent.
From DE 42 32 323 A1, an installation is known for monitoring the thermal treatment of bottles in a bottle treatment machine. In this process, a first sensor is used, which measures the heat radiation emitted by the external surface of the bottle after the sterilization. In the area of introduction of the bottles, before they reach the sterilization installation, the bottles pass a second sensor, which also works on the principle of a pyrometer. An electronic control unit, to which the first and second sensors are connected, determines whether the temperature measured by the first sensor is enough for sufficient sterilization. Such a measuring system requires extensive apparatuses, resulting in high manufacturing costs. In addition, after a time of exposure to steam of only one to two seconds, the temperature increase on the external side of the bottles is extremely small, and it can only be determined with difficulty by the measuring technology. If the treatment of the bottles is carried out with gas or chemical means, for example, ozonizing water, whose temperature is not higher than the temperature of the bottle, or only insignificantly higher than the temperature of the bottle, at the beginning of the treatment, then the known temperature control installation for monitoring the sterilization process is completely unsuited, because in this case there is no detectable temperature increase of the bottle wall.